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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D21, 4670, doi:10.1029/2003JD003584, 2003

Short-term variation of CO₂ flux in relation to environmental controls in an alpine meadow on the Qinghai-Tibetan Plateau

Song Gu

National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan

Yanhong Tang

National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan

Mingyuan Du

National Institute for Agro-Environmental Sciences, Tsukuba, Ibaraki, Japan

Tomomichi Kato

Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan

Yingnian Li

Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining, China

Xiaoyong Cui

National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan

Xingquan Zhao

Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining, China

Abstract

The alpine meadow ecosystem on the Qinghai-Tibetan Plateau may play a significant role in the regional carbon cycle. To assess the CO₂ flux and its relationship to environmental controls in the ecosystem, eddy covariance of CO₂, H₂O, and energy fluxes was measured with an open-path system in an alpine meadow on the plateau at an elevation of 3,250 m. Net ecosystem CO₂ influx (Fc) averaged 8.8 g m⁻² day⁻¹ during the period from August 9 to 31, 2001, with a maximum of 15.9 g m⁻² day⁻¹ and a minimum of 2.3 g m⁻² day⁻¹. Daytime Fc averaged 16.7 g m⁻² day⁻¹ and ranged from 10.4 g m⁻² day⁻¹ to 21.7 g m⁻² day⁻¹ during the study period. For the same photosynthetic photon flux density (PPFD), gross CO₂ uptake (Gc) was significantly higher on cloudy days than on clear days. However, mean daily Gc was higher on clear days than on cloudy days. With high PPFD, Fc decreased as air temperature increased from 10°C to 23°C. The greater the difference between daytime and nighttime air temperatures, the more the sink was strengthened. Daytime average water use efficiency of the ecosystem (WUEe) was 8.7 mg (CO₂)(g H₂O)⁻¹; WUEe values ranged from 5.8 to 15.3 mg (CO₂)(g H₂O)⁻¹. WUEe increased with the decrease in vapor pressure deficit. Daily albedo averaged 0.20, ranging from 0.19 to 0.22 during the study period, and was negatively correlated with daily Fc. Our measurements provided some of the first evidence on CO₂ exchange for a temperate alpine meadow ecosystem on the Qinghai-Tibetan Plateau, which is necessary for assessing the carbon budget and carbon cycle processes for temperate grassland ecosystems.

Received 11 March 2003; accepted 12 August 2003; published 7 November 2003.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0350 Atmospheric Composition and Structure: Pressure, density, and temperature; 1610 Global Change: Atmosphere (0315, 0325); 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 4806 Oceanography: Biological and Chemical: Carbon cycling.

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Citation: Gu, S., Y. Tang, M. Du, T. Kato, Y. Li, X. Cui, and X. Zhao (2003), Short-term variation of CO₂ flux in relation to environmental controls in an alpine meadow on the Qinghai-Tibetan Plateau, J. Geophys. Res., 108(D21), 4670, doi:10.1029/2003JD003584.

Copyright 2003 by the American Geophysical Union.